2014 JAMB Chemistry Past Questions

Questions

1. 1.

   The alkanol obtained from the production of soap is

   1. A.propanol
   2. B.ethanol
   3. C.glycerol
   4. D.methanol

   Show answer

   Answer: C. glycerol

   AI explanation

   Analysis

   The question asks for the specific alkanol (alcohol) produced as a byproduct during the process of soap making, which is chemically known as saponification.

   Concept Explanation

   Saponification is the alkaline hydrolysis of fats and oils (triglycerides). Fats and oils are esters formed from a long-chain fatty acid and a trihydric alcohol called glycerol (also known as propane-1,2,3-triol).

   When a fat or oil reacts with a strong base (like sodium hydroxide, NaOH), the ester bonds are broken. The fatty acid part reacts with the sodium ion to form soap (sodium salt of fatty acid), and the alcohol part is released as a byproduct.

   The general reaction is: Fat/Oil + Sodium Hydroxide → Soap + Glycerol

   Step-by-Step Solution

   1. Identify the reactants: Fats and oils are esters of fatty acids and glycerol.
   2. Understand the reaction: During saponification, the ester linkage is cleaved.
   3. Identify the products: The reaction produces soap (the salt of the fatty acid) and the alcohol that was originally part of the fat molecule.
   4. Determine the alcohol: Since fats and oils are triglycerides, the alcohol released is always glycerol. Glycerol is a polyhydric alcohol (specifically a triol) with the formula $C_3H_8O_3$.

   Comparing this to the options:

   • Propanol is a monohydric alcohol.
   • Ethanol is a monohydric alcohol.
   • Glycerol is the trihydric alcohol produced in this process.
   • Methanol is a monohydric alcohol.

   Conclusion

   Exam Tip

   Remember the "Saponification Rule": Fats/Oils = Soap + Glycerol. Whenever you see a question about soap production, look for "Glycerol" or "Glycerin" as the alcohol byproduct. Don't be confused by the term "alkanol"—while glycerol is a polyhydric alcohol, it is the standard answer for this specific chemical process in JAMB chemistry.

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2. 2.

   Water is said to be temporarily hard when it contains

   1. A.Ca (HCO3)2 and Mg (HCO3)2 salts
   2. B.Ca (HCO3)2 and CaCO3 SALTS
   3. C.Mg(HCO3)2 and CaSO4 salts
   4. D.CaSO4 and Ca(HCO3)2 salts

   Show answer

   Answer: A. Ca (HCO3)2 and Mg (HCO3)2 salts

   AI explanation

   Analysis

   The question asks for the specific chemical composition that makes water "temporarily hard." Hard water is classified into two types: temporary and permanent. Understanding the difference between the two is a common requirement for JAMB Chemistry.

   Concept Explanation

   • Temporary Hardness: This is caused by the presence of dissolved bicarbonates (also known as hydrogen carbonates) of calcium or magnesium. It is called "temporary" because it can be easily removed by boiling the water or by adding slaked lime (calcium hydroxide).
   • Permanent Hardness: This is caused by the presence of chlorides or sulfates of calcium or magnesium. This type of hardness cannot be removed by boiling; it requires chemical treatment (like adding washing soda or using ion-exchange resins).

   Step-by-Step Solution

   1. Identify the cause of temporary hardness: As defined above, temporary hardness is strictly due to the presence of $Ca(HCO_3)_2$ (Calcium bicarbonate) and $Mg(HCO_3)_2$ (Magnesium bicarbonate).
   2. Evaluate the options: • Option A: Contains both bicarbonates. This matches our definition. • Option B: Contains $CaCO_3$ (Calcium carbonate). Calcium carbonate is insoluble in water and does not contribute to hardness. • Option C: Contains $CaSO_4$ (Calcium sulfate). Sulfates cause permanent hardness, not temporary. • Option D: Contains $CaSO_4$. Again, sulfates cause permanent hardness.

   Conclusion

   Since temporary hardness is solely attributed to the bicarbonates of calcium and magnesium, Option A is the correct description.

   Exam Tip

   To remember this easily, think of the "B" in Bicarbonate as standing for Boiling. If you can remove the hardness by Boiling, it must be caused by Bicarbonates!

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3. 3.

   A mixture is different from a compound because

   1. A.the properties of a compound are those of its individual constituents while those of a mixture differ from its constituents
   2. B.a mixture is always homogeneous while a compound is not
   3. C.the constituent of a compound are chemically bound together while those of a mixture are not
   4. D.a mixture can be represented by a chemical formula while a compound cannot

   Show answer

   Answer: C. the constituent of a compound are chemically bound together while those of a mixture are not

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4. 4.

   The dispersion of a liquid in a liquid medium will give

   1. A.an emulsion
   2. B.a fog
   3. C.a gel
   4. D.an aerosol

   Show answer

   Answer: A. an emulsion

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5. 5.

   A gas X diffuses twice as fast as gas Y. if the relative molecular mass of X is 32, calculate the relative molecular mass of Y.

   1. A.128
   2. B.8
   3. C.16
   4. D.64

   Show answer

   Answer: A. 128

   AI explanation

   1. Analyze the question

   We are given the relative rates of diffusion of two gases, X and Y, and the relative molecular mass of gas X. We need to find the relative molecular mass of gas Y. This is a classic application of Graham’s Law of Diffusion.

   2. Explain the concept

   Graham’s Law of Diffusion states that the rate of diffusion ($r$) of a gas is inversely proportional to the square root of its relative molecular mass ($M$):

   $r \propto \frac{1}{\sqrt{M}}$

   When comparing two gases, X and Y, the formula is:

   $\frac{r_X}{r_Y} = \sqrt{\frac{M_Y}{M_X}}$

   Where:

   • $r_X$ and $r_Y$ are the rates of diffusion of gases X and Y.
   • $M_X$ and $M_Y$ are the relative molecular masses of gases X and Y.

   3. Show the solution

   Given:

   • $r_X = 2 \times r_Y$ (Gas X diffuses twice as fast as gas Y)
   • $M_X = 32$
   • $M_Y = ?$

   Step-by-step calculation:

   1. Substitute the known values into the Graham's Law formula: $$\frac{2r_Y}{r_Y} = \sqrt{\frac{M_Y}{32}}$$

   2. The $r_Y$ terms cancel out: $$2 = \sqrt{\frac{M_Y}{32}}$$

   3. Square both sides to remove the square root: $$2^2 = \frac{M_Y}{32}$$ $$4 = \frac{M_Y}{32}$$

   4. Solve for $M_Y$: $$M_Y = 4 \times 32$$ $$M_Y = 128$$

   4. Identify the answer

   The calculated relative molecular mass of gas Y is 128. This matches option A.

   5. Exam Tip

   When using Graham's Law, always remember the "Inverse Relationship" rule: the faster gas is always on top of the rate ratio, but its mass is on the bottom of the square root ratio. A common mistake is to flip the masses; if you get a mass that is smaller than expected for a slower gas, check your formula setup!

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6. 6.

   The major and most effective way of controlling pollution is to

   1. A.improve machinery so that the substances released from combustion are less harmful
   2. B.pass strict laws against it by individuals and companies
   3. C.educate people on the causes and effects of pollution
   4. D.convert chemical wastes to harmless substances before releasing them into the environment

   Show answer

   Answer: C. educate people on the causes and effects of pollution

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7. 7.

   In the electrolytic extraction of calcium from calcium chloride, the cathode is

   1. A.zinc
   2. B.graphite
   3. C.platinum
   4. D.iron

   Show answer

   Answer: D. iron

   AI explanation

   Analysis

   The question asks for the material used as the cathode during the electrolytic extraction of calcium from molten calcium chloride ($CaCl_2$).

   Concept Explanation

   In the industrial extraction of calcium by electrolysis, the electrolyte is molten calcium chloride. Because calcium is a highly reactive metal, it cannot be extracted from aqueous solutions (as hydrogen would be discharged instead).

   During this process:

   • The Anode: Usually made of graphite, where chloride ions are oxidized to chlorine gas.
   • The Cathode: This is where calcium ions ($Ca^{2+}$) are reduced to metallic calcium ($Ca$).

   In this specific industrial setup, the cathode is typically made of iron. The molten calcium collects on the iron cathode, which is often kept at a temperature just above the melting point of calcium so that the metal can be tapped off.

   Step-by-Step Solution

   1. Identify the process: Electrolytic extraction of calcium from molten $CaCl_2$.
   2. Understand the components: The cell requires an inert or suitable metal for the electrodes.
   3. Evaluate the cathode: In the standard industrial method (the Downs cell or similar electrolytic processes for alkaline earth metals), an iron rod or iron lining is used as the cathode because it is durable and does not readily react with the molten calcium at the operating temperatures.
   4. Compare with options: • Zinc (A) is not used as a cathode here. • Graphite (B) is typically used as the anode. • Platinum (C) is an inert electrode but is too expensive for large-scale industrial extraction. • Iron (D) is the standard material used for the cathode in this process.

   Conclusion

   Exam Tip

   When studying electrolysis, always remember the "Anode-Oxidation, Cathode-Reduction" (A-O-C-R) rule. Also, for industrial extractions, remember that graphite is almost always the anode (because it can withstand the chlorine gas produced), while iron or steel is commonly used as the cathode for reactive metals.

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8. 8.

   Zn (s) + CuSO 4(aq) → ZnSO 4(aq) + Cu (s) In the reaction above, the oxidation number of the reducing agent changes from

   1. A.0 to + 4
   2. B.0 to + 2
   3. C.+ 1 to + 2
   4. D.+ 1 to + 3

   Show answer

   Answer: B. 0 to + 2

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9. 9.

   CH3COOC2H5(1) + H2O(1) ⇌ CH 3COOH (aq) + C 2H 5OH (aq) The purpose of H+ in the reaction above is to

   1. A.increase the yield of products
   2. B.maintain the solution at a constant PH
   3. C.increase the rate of the hydrolysis
   4. D.decrease the rate of the reverse reaction

   Show answer

   Answer: C. increase the rate of the hydrolysis

   AI explanation

   Analysis of the Question

   The reaction provided is the acid-catalyzed hydrolysis of an ester (ethyl ethanoate). You are asked to identify the specific role of the hydrogen ion ($H^+$) in this chemical equation.

   Concept Explanation

   In organic chemistry, esters react with water to form a carboxylic acid and an alcohol. This process is known as hydrolysis.

   1. Nature of the Reaction: The hydrolysis of an ester is a relatively slow process at room temperature.
   2. Role of the Catalyst: The $H^+$ ion acts as a catalyst. A catalyst is a substance that increases the rate of a chemical reaction without being consumed in the process. It does this by providing an alternative reaction pathway with a lower activation energy.
   3. Equilibrium: While catalysts speed up reactions, they do not change the position of the equilibrium (i.e., they do not increase the yield of the products; they only help the system reach equilibrium faster).

   Step-by-Step Solution

   • Step 1: Identify the reactants and products. We have an ester ($CH_3COOC_2H_5$) reacting with water ($H_2O$) to produce ethanoic acid ($CH_3COOH$) and ethanol ($C_2H_5OH$).
   • Step 2: Recognize the catalyst. The $H^+$ represents an acid catalyst (such as dilute $H_2SO_4$ or $HCl$).
   • Step 3: Evaluate the options based on the definition of a catalyst: • A: Incorrect. Catalysts do not increase the yield (the amount of product formed at equilibrium); they only speed up the attainment of that equilibrium. • B: Incorrect. While acids affect pH, the primary purpose of adding $H^+$ to this specific reaction is to speed it up. • C: Correct. The $H^+$ ion lowers the activation energy, thereby increasing the rate at which the ester is hydrolyzed into acid and alcohol. • D: Incorrect. A catalyst increases the rate of both the forward and reverse reactions equally.

   Conclusion

   The $H^+$ ion acts as a catalyst to speed up the hydrolysis process. Therefore, its purpose is to increase the rate of the reaction.

   Exam Tip: Whenever you see a small $H^+$ written above the arrow in a chemical equation, always associate it with catalysis (speeding up the reaction). Never confuse a catalyst with a reactant that increases yield!

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10. 10.

    The process of converting starch to ethanol is

    1. A.cracking
    2. B.distillation
    3. C.fermentation
    4. D.oxidation

    Show answer

    Answer: C. fermentation

    AI explanation

    Analysis

    The question asks for the specific chemical process used to transform starch (a complex carbohydrate) into ethanol (an alcohol).

    Concept Explanation

    To convert starch into ethanol, the process happens in two main stages:

    1. Hydrolysis: Starch is first broken down into simpler sugars (like glucose) using enzymes (such as amylase found in malt).
    2. Fermentation: The glucose is then converted into ethanol and carbon(IV) oxide by the action of enzymes (zymase) present in yeast.

    • Cracking refers to breaking down large hydrocarbon molecules into smaller ones (common in petroleum refining).
    • Distillation is a physical process used to separate mixtures based on boiling points (often used to purify the ethanol produced after fermentation).
    • Oxidation involves the loss of electrons or an increase in oxidation state (e.g., converting ethanol to ethanoic acid).

    Step-by-Step Solution

    1. Identify the starting material: Starch $(C_6H_{10}O_5)_n$.
    2. Identify the product: Ethanol $(C_2H_5OH)$.
    3. Identify the mechanism: The biological breakdown of sugars by yeast enzymes is defined as fermentation.
    4. Evaluate the options: • A (Cracking) is for hydrocarbons. • B (Distillation) is for separation, not conversion. • C (Fermentation) is the biological conversion of sugars to alcohol. • D (Oxidation) is the reverse of reduction or the conversion of alcohols to acids.

    The process of converting starch to ethanol is clearly defined as fermentation.

    Exam Tip

    Whenever you see "starch," "sugar," or "glucose" being converted into "ethanol" or "alcohol" in a chemistry question, the answer is almost always fermentation. Remember that yeast is the biological catalyst (enzyme) required for this reaction!

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11. 11.

    Polystyrene is widely used as packaging materials for fragile objects during transportation because of its

    1. A.lightness
    2. B.low density
    3. C.high density
    4. D.high compressibility

    Show answer

    Answer: D. high compressibility

    AI explanation

    Analysis of the Question

    The question asks for the specific physical property of polystyrene that makes it ideal for packaging fragile items. We need to evaluate the options based on the material's structural characteristics and its function in protecting goods from impact.

    Concept Explanation

    Polystyrene, especially in its expanded form (often called Styrofoam), is a polymer made from styrene monomers. When manufactured for packaging, it is processed into a foam structure containing many trapped air pockets.

    • Density vs. Compressibility: While polystyrene is indeed light and has low density, those properties alone do not explain why it is used for protection.
    • The Role of Compressibility: When an object is wrapped in a material, the goal is to absorb kinetic energy during a collision or drop. A material that is highly compressible can deform under pressure, effectively increasing the time over which the impact force is applied to the fragile object. This reduces the impulse (force) experienced by the object, preventing it from breaking.

    Step-by-Step Solution

    1. Evaluate A and B: Polystyrene is light and has low density, which makes shipping cheaper, but these properties do not provide shock absorption.
    2. Evaluate C: High density would make the material hard and rigid, which would likely transmit impact forces directly to the fragile object rather than absorbing them.
    3. Evaluate D: Because of its foam structure, polystyrene is highly compressible. When a force is applied (like a drop), the air pockets collapse, absorbing the energy of the impact. This cushioning effect is the primary reason it is used for packaging.

    Conclusion

    While polystyrene is light (low density), its ability to compress and absorb mechanical shock is the functional reason it is used to protect fragile items.

    Exam Tip

    When you see questions about packaging materials in Chemistry or Physics, look for terms related to energy absorption or cushioning. Materials that are "compressible" or "elastic" are usually the correct answers for shock protection, whereas "dense" or "hard" materials are used for structural support.

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12. 12.

    The IUPAC nomenclature of the compound above is

    1. A.2-bromo-3-chlorobutanol
    2. B.3-bromo-2-chlorobutanol
    3. C.3-chloro-2-bromobutanol
    4. D.2-chloro-3-bromobutanol

    Show answer

    Answer: B. 3-bromo-2-chlorobutanol

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13. 13.

    In an equilibrium reaction, which of the following conditions indicates that maximum yield of the product will be obtained?

    1. A.Equilibrium constant is very large
    2. B.∆H - T∆S = O
    3. C.∆ H > T ∆ S
    4. D.Equilibrium constant is less than zero

    Show answer

    Answer: A. Equilibrium constant is very large

    AI explanation

    Analysis

    The question asks for the condition that signifies the maximum yield of products in a chemical equilibrium reaction. We need to relate the equilibrium constant ($K$) to the spontaneity and extent of the reaction.

    Concept Explanation

    In chemical thermodynamics, the relationship between the standard Gibbs free energy change ($\Delta G^\circ$) and the equilibrium constant ($K$) is given by the equation:

    $\Delta G^\circ = -RT \ln K$

    • If $K$ is very large ($K \gg 1$): The value of $\ln K$ is a large positive number. This makes $\Delta G^\circ$ a large negative number. A large negative $\Delta G^\circ$ indicates that the reaction is spontaneous and proceeds far to the right, favoring the formation of products. Therefore, a large $K$ means the equilibrium position lies heavily toward the product side, resulting in a maximum yield.
    • If $K$ is very small ($K \ll 1$): The value of $\ln K$ is a large negative number, making $\Delta G^\circ$ positive. This indicates the reaction is non-spontaneous and favors the reactants, resulting in a low yield.
    • Regarding $\Delta G = \Delta H - T\Delta S$: For a reaction to be spontaneous, $\Delta G$ must be negative. Setting $\Delta H - T\Delta S = 0$ actually represents the point of equilibrium where the system is neither moving forward nor backward, not the condition for maximum product yield.

    Step-by-Step Solution

    1. Evaluate the relationship: The yield of a product in an equilibrium reaction is determined by the position of equilibrium.
    2. Analyze the equilibrium constant ($K$): $K = \frac{[\text{Products}]}{[\text{Reactants}]}$. For the yield of products to be maximum, the numerator must be much larger than the denominator. This mathematically results in a very large value for $K$.
    3. Check the options: • Option A: A large $K$ implies the concentration of products is significantly higher than reactants at equilibrium. This is correct. • Option B: $\Delta H - T\Delta S = 0$ means $\Delta G = 0$, which is the definition of the equilibrium state itself, not a condition for maximum yield. • Option C: $\Delta H > T\Delta S$ implies $\Delta G > 0$, meaning the reaction is non-spontaneous and will not favor products. • Option D: An equilibrium constant cannot be less than zero (it must be a positive value).

    Conclusion

    The condition that indicates the maximum yield of products is a very large equilibrium constant, as it shows the reaction strongly favors the product side.

    Exam Tip: Always remember the "K-Rule": If $K > 1$, products are favored (high yield). If $K < 1$, reactants are favored (low yield). If $K = 1$, the concentration of products and reactants is roughly equal.

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14. 14.

    In the extraction of sodium from fused sodium chloride, the anode is made of platinum because

    1. A.sodium is formed at the anode
    2. B.chlorine is formed at the anode
    3. C.sodium does not react with platinum
    4. D.chlorine does not react with platinum

    Show answer

    Answer: D. chlorine does not react with platinum

    AI explanation

    Analysis of the Question

    This question tests your understanding of the Downs Cell process, which is the industrial method used for the extraction of sodium metal from molten (fused) sodium chloride ($NaCl$). You are specifically asked why platinum is chosen as the material for the anode.

    Concept Explanation

    In the electrolysis of fused sodium chloride:

    • The Electrolyte: Molten $NaCl$ dissociates into ions: $NaCl \rightarrow Na^+ + Cl^-$.
    • The Cathode (Negative Electrode): Sodium ions ($Na^+$) migrate to the cathode, where they gain electrons to form sodium metal ($Na^+ + e^- \rightarrow Na$).
    • The Anode (Positive Electrode): Chloride ions ($Cl^-$) migrate to the anode, where they lose electrons to form chlorine gas ($2Cl^- \rightarrow Cl_2 + 2e^-$).

    Because chlorine gas is a highly reactive non-metal and a strong oxidizing agent, it can easily corrode many common metals. Therefore, the material chosen for the anode must be chemically inert (unreactive) toward the chlorine gas being produced at its surface.

    Step-by-Step Solution

    1. Identify the product at the anode: As established, chlorine gas ($Cl_2$) is liberated at the anode.
    2. Evaluate the reactivity: If the anode were made of a reactive metal, the chlorine gas would react with the electrode, causing it to dissolve or corrode, which would contaminate the product and destroy the electrode.
    3. Why Platinum? Platinum is a noble metal. It is highly resistant to chemical attack and oxidation. Even in the presence of hot, corrosive chlorine gas, platinum remains stable and does not react.
    4. Reviewing the options: • Option A is incorrect because sodium is formed at the cathode, not the anode. • Option B is a true statement (chlorine is formed at the anode), but it does not explain why platinum is used as the material. • Option C is irrelevant because sodium is not formed at the anode. • Option D explains the chemical necessity: the anode must be made of a material that does not react with the chlorine gas produced.

    Conclusion

    The choice of platinum is specifically to prevent the corrosion of the anode by the chlorine gas being evolved.

    Final Answer: The correct option is D.

    Exam Tip: In electrolysis questions, always remember the mnemonic PANIC: Positive Anode, Negative Is Cathode. Also, remember that in the Downs Cell, the anode is actually made of graphite in industrial practice to save costs, but if platinum is mentioned in a theoretical context, it is because of its chemical inertness toward chlorine.

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15. 15.

    If the change in free energy of a system is -899 J$mol^{-1}$ and the entropy change is 10J$mol^{-1}$k-1 at 250C, calculate the enthalpy change.

    1. A.+2081 J$mol^{-1}$
    2. B.-2081 J$mol^{-1}$
    3. C.-649 J$mol^{-1}$
    4. D.+649 J$mol^{-1}$

    Show answer

    Answer: A. +2081 J$mol^{-1}$

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16. 16.

    Due to the unstable nature of ethyne, it is stored by dissolving in

    1. A.ethane-1,2-diol
    2. B.propanol
    3. C.ethanoic acid
    4. D.propanone

    Show answer

    Answer: D. propanone

    AI explanation

    1. Analyze the question

    The question asks for the specific solvent used to safely store ethyne (acetylene) gas. Ethyne is highly unstable and can explode if compressed or stored in its pure form under pressure.

    2. Explain the concept

    Ethyne ($C_2H_2$) is an alkyne that is highly reactive and thermally unstable. When subjected to high pressure, it can undergo explosive decomposition. To transport and store it safely, it is dissolved in a solvent that can hold large volumes of the gas without reacting with it.

    The industry standard for this is propanone (also known as acetone). Propanone has a high capacity for dissolving ethyne; at a pressure of about 15 atmospheres, one volume of propanone can dissolve about 300 volumes of ethyne. The gas is usually stored in cylinders filled with a porous material (like diatomaceous earth) soaked in propanone.

    3. Show the solution

    • Step 1: Identify the chemical properties of ethyne. It is a highly flammable and unstable gas.
    • Step 2: Evaluate the options provided: • Ethane-1,2-diol: Used as an antifreeze, not for gas storage. • Propanol: An alcohol, not the standard solvent for ethyne. • Ethanoic acid: A carboxylic acid that would react with many substances and is not suitable for this purpose. • Propanone (Acetone): A ketone that is chemically inert toward ethyne and has a very high solubility for the gas, making it the ideal medium for safe storage.
    • Step 3: Conclude that propanone is the correct solvent used in industrial gas cylinders.

    4. Identify the answer

    The correct option is D.

    5. Exam Tip

    When you see questions about ethyne (acetylene) in your JAMB or WASSCE exams, always associate it with propanone (acetone). Also, remember that ethyne is produced by the reaction of calcium carbide ($CaC_2$) with water. These two facts are frequently tested together!

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17. 17.

    How many protons, neutrons and electrons respectively are present in the element 60/27 Co?

    1. A.27, 33 and 33
    2. B.33, 27 and 27
    3. C.27, 33, and 27
    4. D.60, 33 and 60

    Show answer

    Answer: C. 27, 33, and 27

    AI explanation

    Analysis

    To solve this, we need to understand the notation for an atom, which is written as $^A_Z X$:

    • $X$ is the chemical symbol of the element.
    • $A$ is the Mass Number (the sum of protons and neutrons).
    • $Z$ is the Atomic Number (the number of protons).

    For the element $^{60}_{27}\text{Co}$:

    • $A = 60$
    • $Z = 27$

    Concept

    1. Protons: The atomic number ($Z$) always equals the number of protons.
    2. Electrons: In a neutral atom (like this one), the number of electrons is equal to the number of protons.
    3. Neutrons: The number of neutrons is calculated by subtracting the atomic number from the mass number: $\text{Neutrons} = A - Z$.

    Step-by-Step Solution

    1. Find Protons: The atomic number is 27, so there are 27 protons.
    2. Find Electrons: Since the atom is neutral, the number of electrons equals the number of protons, so there are 27 electrons.
    3. Find Neutrons: Subtract the atomic number from the mass number: • $\text{Neutrons} = 60 - 27 = 33$ • There are 33 neutrons.

    Putting them in the requested order (protons, neutrons, electrons): 27, 33, 27.

    Conclusion

    Comparing our result to the options provided:

    • A: 27, 33, 33 (Incorrect)
    • B: 33, 27, 27 (Incorrect)
    • C: 27, 33, 27 (Correct)
    • D: 60, 33, 60 (Incorrect)

    Exam Tip

    Always remember the acronym APE:

    • Atomic number = Protons = Electrons.
    • To find Neutrons, just subtract the atomic number from the mass number (N = M - A). This simple trick will save you time in the exam hall!

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18. 18.

    The colour of litmus in a neutral medium is

    1. A.purple
    2. B.pink
    3. C.yellow
    4. D.orange

    Show answer

    Answer: A. purple

    AI explanation

    Analysis

    The question asks for the specific color of litmus paper or litmus solution when it is in a neutral medium (neither acidic nor basic).

    Concept Explanation

    Litmus is a water-soluble mixture of different dyes extracted from lichens. It is commonly used as an acid-base indicator in chemistry laboratories. Its color changes depending on the pH of the solution it is placed in:

    • In Acidic medium: Litmus turns red.
    • In Basic (alkaline) medium: Litmus turns blue.
    • In Neutral medium: Litmus maintains its natural color, which is purple.

    Step-by-Step Solution

    1. Identify the nature of the medium: The question specifies a "neutral medium," meaning the pH is approximately 7.
    2. Recall indicator properties: Litmus is unique because its original state is purple. When it reacts with hydrogen ions ($H^+$) in acids, it shifts toward red; when it reacts with hydroxide ions ($OH^-$) in bases, it shifts toward blue.
    3. Determine the color: Since there is no excess of $H^+$ or $OH^-$ ions in a neutral medium to cause a shift, the litmus remains in its original, neutral color, which is purple.

    Conclusion

    Comparing this to the provided options:

    • A. purple (Correct)
    • B. pink (Usually associated with phenolphthalein in base)
    • C. yellow (Associated with methyl orange in base)
    • D. orange (Associated with methyl orange in neutral/acidic conditions)

    Exam Tip: To remember this easily, think of the primary colors: Red (Acid) + Blue (Base) = Purple (Neutral). Keep this "color mixing" logic in mind for your chemistry practicals!

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19. 19.

    The petroleum fraction that is used in heating furnaces in industries is

    1. A.diesel oil
    2. B.gasoline
    3. C.kerosene
    4. D.lubricating oil

    Show answer

    Answer: A. diesel oil

    AI explanation

    Analysis

    The question asks for the specific petroleum fraction used primarily as fuel for heating furnaces in industrial settings. To answer this, we must look at the boiling point ranges and the typical applications of the various fractions obtained from the fractional distillation of crude oil.

    Concept Explanation

    When crude oil is refined, it is separated into different fractions based on their boiling points. Each fraction has a specific use:

    • Gasoline (Petrol): Used primarily as fuel for internal combustion engines (cars).
    • Kerosene (Paraffin): Used for domestic heating, cooking, and as jet fuel.
    • Diesel Oil (Gas Oil): Used as fuel for heavy-duty engines (trucks, buses, trains) and, crucially, as a fuel for industrial heating furnaces and boilers.
    • Lubricating Oil: Used to reduce friction in machinery and engines.

    Step-by-Step Solution

    1. Evaluate Gasoline: While highly flammable, it is too volatile and expensive for large-scale industrial furnace heating.
    2. Evaluate Kerosene: It is used for heating, but it is generally reserved for domestic purposes (stoves/lamps) and aviation.
    3. Evaluate Diesel Oil: Diesel oil has a higher boiling point than gasoline and kerosene. It provides a high energy density, making it the standard choice for industrial burners, furnaces, and large boilers where sustained, high-temperature heat is required.
    4. Evaluate Lubricating Oil: This is a thick, viscous substance used for lubrication, not as a fuel for combustion.

    Comparing these, diesel oil is the fraction specifically processed and marketed for industrial heating applications.

    Conclusion

    The petroleum fraction used in heating furnaces in industries is diesel oil.

    Exam Tip: Remember the order of fractions from the top of the fractionating column to the bottom: Refinery gases → Gasoline → Kerosene → Diesel → Lubricating oil → Bitumen. As you go down the column, the molecules get larger, the boiling point increases, and the substances become more viscous (thicker).

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20. 20.

    A hydrocarbon has an empirical formula CH and a vapour density of 39. Determine its molecular formula. [C = 12, H = 1]

    1. A.C2H6
    2. B.C3H8
    3. C.C3H4
    4. D.C6H6

    Show answer

    Answer: D. C6H6

    AI explanation

    To determine the molecular formula of the hydrocarbon, we follow these steps:

    1. Analyze the Question

    We are given:

    • Empirical formula = $\text{CH}$
    • Vapour density = $39$
    • Atomic masses: $\text{C} = 12, \text{H} = 1$
    • Goal: Find the molecular formula.

    2. Explain the Concept

    • Molecular Mass: The molecular mass of a substance is twice its vapour density. $$\text{Molecular Mass} = 2 \times \text{Vapour Density}$$
    • Relationship: The molecular formula is a multiple of the empirical formula. If $n$ is the multiplier, then: $$\text{Molecular Formula} = (\text{Empirical Formula})_n$$ $$\text{Molecular Mass} = n \times (\text{Empirical Formula Mass})$$

    3. Show the Solution

    Step 1: Calculate the molecular mass.

    $\text{Molecular Mass} = 2 \times 39 = 78$

    Step 2: Calculate the empirical formula mass.

    $\text{Empirical Formula} = \text{CH}$

    $\text{Mass} = 12 (\text{for C}) + 1 (\text{for H}) = 13$

    Step 3: Find the value of $n$.

    $n = \frac{\text{Molecular Mass}}{\text{Empirical Formula Mass}}$

    $n = \frac{78}{13} = 6$

    Step 4: Determine the molecular formula. Multiply the empirical formula ($\text{CH}$) by $n = 6$:

    $\text{Molecular Formula} = (\text{CH})_6 = \text{C}_6\text{H}_6$

    4. Identify the Answer

    Comparing our result with the given options, $\text{C}_6\text{H}_6$ corresponds to option D.

    5. Exam Tip

    Always remember the relationship Molecular Mass = 2 × Vapour Density. This is a classic JAMB question pattern. If you ever forget the formula, just remember that the molecular mass of Hydrogen gas ($\text{H}_2$) is 2, and its vapour density is 1, which confirms the "times 2" rule!

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21. 21.This question needs a diagram, table or passage that we don't have yet, so it isn't shown.

22. 22.

    Which of the following salts will turn blue litmus red?

    1. A.Sodium tetrahydroxozincate (ll)
    2. B.Sodium hydrogentetraoxosulphate (VI)
    3. C.Sodium trioxocarbonate (lV)
    4. D.Zinc chloride hydroxide

    Show answer

    Answer: B. Sodium hydrogentetraoxosulphate (VI)

    Get a step-by-step AI explanation in the appGet a step-by-step AI explanation in the app

23. 23.

    Ethyne is passed through a hot tube containing organo-nickel catalyst to produce

    1. A.isoprene
    2. B.polythene
    3. C.ethanol
    4. D.benzene

    Show answer

    Answer: D. benzene

    AI explanation

    Analysis

    The question asks for the product formed when ethyne (acetylene) undergoes a specific reaction involving a hot tube and an organo-nickel catalyst. This is a classic organic chemistry reaction known as cyclic polymerization (or trimerization).

    Concept Explanation

    Ethyne ($C_2H_2$) is an unsaturated hydrocarbon with a triple bond. When three molecules of ethyne are passed through a hot tube (usually at about 400°C) in the presence of an organo-nickel catalyst, they undergo a process called cyclotrimerization.

    In this reaction, the three ethyne molecules link together to form a stable, six-carbon cyclic ring. This process converts the aliphatic hydrocarbon (ethyne) into an aromatic hydrocarbon.

    The chemical equation for this reaction is: $3C_2H_2 \xrightarrow{\text{hot tube/catalyst}} C_6H_6$

    Step-by-Step Solution

    1. Identify the reactants: We have ethyne ($C_2H_2$).
    2. Identify the process: Passing ethyne through a hot tube with a catalyst triggers the trimerization of the molecules.
    3. Calculate the product: • 3 molecules of $C_2H_2$ contain a total of 6 carbon atoms and 6 hydrogen atoms. • $3 \times (C_2H_2) = C_6H_6$.
    4. Name the product: The chemical formula $C_6H_6$ corresponds to benzene, which is the simplest aromatic hydrocarbon.

    Conclusion

    • Isoprene is a precursor for natural rubber.
    • Polythene is formed by the polymerization of ethene ($C_2H_4$).
    • Ethanol is an alcohol produced by the hydration of ethene or fermentation.
    • Benzene is the result of the cyclic trimerization of ethyne.

    Exam Tip

    Whenever you see "ethyne" and "hot tube" in a chemistry question, immediately think of benzene. It is a very common JAMB question! Remember: 3 molecules of ethyne = 1 molecule of benzene.

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24. 24.

    A compound that gives a brick-red colour to a non-luminous flame is likely to contain

    1. A.copper ions
    2. B.sodium ions
    3. C.calcium ions
    4. D.Potassium ions

    Show answer

    Answer: C. calcium ions

    AI explanation

    Analysis

    The question asks for the identification of a metal ion based on the characteristic color it imparts to a non-luminous Bunsen flame. This is a classic Flame Test question in inorganic chemistry.

    Concept: Flame Test

    The flame test is an analytical procedure used in chemistry to detect the presence of certain metal ions based on the characteristic emission spectrum produced by each element when heated in a flame. When an element is heated, its electrons absorb energy and jump to higher energy levels. As they return to their ground state, they emit light at specific wavelengths, which we perceive as distinct colors.

    Here are the common flame test colors for the ions listed:

    • Copper ions ($Cu^{2+}$): Produce a blue-green flame.
    • Sodium ions ($Na^+$): Produce an intense golden-yellow flame.
    • Calcium ions ($Ca^{2+}$): Produce a brick-red (or orange-red) flame.
    • Potassium ions ($K^+$): Produce a lilac (or pale violet) flame.

    Step-by-Step Solution

    1. Identify the requirement: We are looking for the ion that produces a "brick-red" flame.
    2. Evaluate the options: • Option A (Copper) is incorrect because it gives a green flame. • Option B (Sodium) is incorrect because it gives a yellow flame. • Option C (Calcium) matches the description of a brick-red flame. • Option D (Potassium) is incorrect because it gives a lilac flame.
    3. Conclusion: Based on standard flame test observations, calcium compounds are the ones responsible for the brick-red coloration.

    Exam Tip

    To remember these colors easily, use a mnemonic:

    • Sodium = Sun (Yellow)
    • Calcium = Carrot (Brick-red/Orange)
    • Potassium = Purple/Lilac
    • Copper = Color of the sea (Blue-green)

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25. 25.

    The general formula of haloalkanes where X represents the halide is

    1. A.Cn H 2n-1X.
    2. B.C nH 2nX.
    3. C.C nH 2n+2 X
    4. D.C nH 2n+1X

    Show answer

    Answer: D. C nH 2n+1X

    AI explanation

    Analysis of the Question

    The question asks for the general molecular formula of haloalkanes (also known as alkyl halides). These are organic compounds derived from alkanes where one or more hydrogen atoms have been replaced by a halogen atom (represented by X).

    Concept Explanation

    1. Alkanes: The general formula for a saturated alkane is $C_nH_{2n+2}$.
    2. Formation of Haloalkanes: To form a mono-haloalkane, you remove one hydrogen atom from an alkane molecule and replace it with a halogen atom (X).
    3. Derivation: • Start with the alkane formula: $C_nH_{2n+2}$ • Subtract one hydrogen: $C_nH_{(2n+2)-1}$ which simplifies to $C_nH_{2n+1}$ • Add the halogen atom (X): $C_nH_{2n+1}X$

    Step-by-Step Solution

    • Step 1: Identify the parent hydrocarbon. Since haloalkanes are derived from alkanes, we start with the alkane general formula: $C_nH_{2n+2}$.
    • Step 2: Apply the substitution rule. Replacing one hydrogen atom with a halogen (X) means we subtract 1 from the hydrogen count ($2n+2 - 1 = 2n+1$).
    • Step 3: Combine the components. We get $C_nH_{2n+1} + X$, which is written as $C_nH_{2n+1}X$.

    Comparing this to the given options:

    • A: $C_nH_{2n-1}X$ (Incorrect)
    • B: $C_nH_{2n}X$ (Incorrect)
    • C: $C_nH_{2n+2}X$ (Incorrect - this would imply an extra bond)
    • D: $C_nH_{2n+1}X$ (Correct)

    Conclusion

    The general formula for a mono-haloalkane is $C_nH_{2n+1}X$. This matches option D.

    Exam Tip

    Always remember that haloalkanes are "alkane-like." If you ever forget the formula, just pick a simple alkane like Methane ($CH_4$). Replace one Hydrogen with Chlorine ($Cl$) to get Chloromethane ($CH_3Cl$). Now, test the options by plugging in $n=1$:

    • For $n=1$, $C_1H_{2(1)+1}X = CH_3X$. This matches our example!

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26. 26.

    The polymer used in making car rear lights is

    1. A.perspex
    2. B.bakeelite
    3. C.polystyrene
    4. D.polyacrylonitrile

    Show answer

    Answer: A. perspex

    AI explanation

    Analysis

    The question asks for the specific type of polymer used in the manufacturing of car rear lights. This requires knowledge of the properties and common industrial applications of various synthetic polymers.

    Concept Explanation

    To solve this, we look at the characteristics of the polymers listed:

    • Perspex (Polymethyl methacrylate - PMMA): This is a transparent, rigid, and durable thermoplastic. Because of its high optical clarity and resistance to weathering, it is widely known as "acrylic glass." It is the standard material used for lenses, car rear lights, and windshields.
    • Bakelite (Phenol-formaldehyde resin): This is a thermosetting plastic. It is opaque, hard, and heat-resistant, commonly used for electrical fittings like switch plates and handles for cooking pots.
    • Polystyrene: This is a versatile plastic used for making disposable cups, food containers, and packaging materials (like Styrofoam). It is generally not used for car lights because it is not as durable or weather-resistant as PMMA.
    • Polyacrylonitrile (PAN): This is primarily used in the production of synthetic fibers (like acrylic wool) for clothing and carpets.

    Step-by-Step Solution

    1. Identify the requirement: Car rear lights need to be transparent, shatter-resistant, and able to withstand outdoor environmental conditions (sunlight and rain).
    2. Evaluate the options: • Bakelite is opaque (not suitable for lights). • Polyacrylonitrile is used for fibers (not suitable for rigid light casings). • Polystyrene is brittle and lacks the necessary optical clarity and weather resistance for automotive exterior use. • Perspex (PMMA) is specifically engineered for high transparency and strength, making it the ideal material for automotive lighting.
    3. Conclusion: Based on the properties of these polymers, Perspex is the correct material used for car rear lights.

    Exam Tip

    When dealing with polymer questions in JAMB, remember the "Big Three" applications:

    • Perspex: Transparent, glass-like (lights, windows).
    • Bakelite: Heat-resistant, electrical insulator (switches, handles).
    • Polythene/Polystyrene: Packaging and containers.

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27. 27.

    An element X has electron configuration 1s2 2s2 2p6 3s2 3p5. Which of the following statements is correct about the element?

    1. A.lt has a completely filled p-orbital
    2. B.lt has 5 electrons in its outermost shell.
    3. C.lt belongs to group ll on the periodic table
    4. D.lt is a halogen

    Show answer

    Answer: D. lt is a halogen

    AI explanation

    1. Analyze the Question

    We are given the electronic configuration of an element X: $1s^2 2s^2 2p^6 3s^2 3p^5$. We need to determine its chemical properties and position in the periodic table based on this configuration.

    2. Explain the Concept

    • Determining the Group: The group of an element is determined by the total number of electrons in its outermost shell (valence shell). For this element, the highest principal quantum number is 3. The electrons in the 3rd shell are $3s^2$ and $3p^5$. • Total valence electrons = $2 + 5 = 7$. • Elements with 7 valence electrons belong to Group 7 (or Group VII).
    • Identifying the Element: Elements in Group 7 are known as Halogens. They are highly reactive non-metals that need one more electron to achieve a stable octet configuration (a full shell).
    • Orbital Filling: A "completely filled p-orbital" would mean the p-subshell contains 6 electrons ($p^6$). Here, we have $p^5$, meaning it is one electron short of being full.

    3. Show the Solution

    • Step 1: Identify the valence shell. The configuration ends in $3s^2 3p^5$. The valence shell is the 3rd shell.
    • Step 2: Count the valence electrons. $2 (from\ s) + 5 (from\ p) = 7$ electrons.
    • Step 3: Evaluate the options: • A: Incorrect. It has 5 electrons in the p-orbital, not 6. It is one electron short of being filled. • B: Incorrect. It has 7 electrons in its outermost shell, not 5. • C: Incorrect. Elements in Group II have 2 valence electrons (ending in $ns^2$). • D: Correct. Elements with 7 valence electrons are classified as halogens.

    4. Identify the Answer

    Based on the analysis, the element is a halogen because it has 7 valence electrons and requires one electron to complete its octet.

    5. Exam Tip

    The "Octet Rule" Shortcut: For elements in the p-block (Groups 13–18), you can quickly find the group number by adding 10 to the number of valence electrons. Here, $7 + 10 = 17$. Group 17 is the Halogen group. Remember: Halogens ($F, Cl, Br, I$) always end in $ns^2 np^5$.

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28. 28.

    Fluorine does not occur in the free state in nature because

    1. A.it is a poisonous gas
    2. B.it belongs to the halogen family
    3. C.it is inert
    4. D.of its high reactivity

    Show answer

    Answer: D. of its high reactivity

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29. 29.

    Beryllium and aluminum have similar properties because they?

    1. A.are both metals
    2. B.belong to the same group
    3. C.belong to the same period
    4. D.are positioned diagonally to each other

    Show answer

    Answer: D. are positioned diagonally to each other

    AI explanation

    Analysis

    This question tests your knowledge of the Periodic Table and the concept of Diagonal Relationships. You are being asked why Beryllium ($Be$) and Aluminum ($Al$) exhibit similar chemical properties despite being in different groups and periods.

    Concept: Diagonal Relationship

    In the periodic table, certain elements in the second period show a striking similarity to the element located diagonally to their right in the third period. This is known as a diagonal relationship.

    The primary reasons for this similarity are:

    1. Charge-to-size ratio (Ionic Potential): As you move across a period, the atomic size decreases and the charge increases. As you move down a group, the size increases. These two trends cancel each other out when moving diagonally, resulting in similar ionic potentials.
    2. Electronegativity: The electronegativity values of these diagonal pairs are very similar, which leads to similar bonding characteristics (e.g., both form covalent bonds rather than purely ionic ones).

    Examples of diagonal pairs:

    • Lithium ($Li$) and Magnesium ($Mg$)
    • Beryllium ($Be$) and Aluminum ($Al$)
    • Boron ($B$) and Silicon ($Si$)

    Step-by-Step Explanation

    1. Check Group/Period: Beryllium is in Group 2, Period 2. Aluminum is in Group 13, Period 3. Since they are in different groups and periods, options B and C are incorrect.
    2. Check Metal Status: While both are metals, many elements are metals but do not share the specific chemical properties that $Be$ and $Al$ share (such as their oxides being amphoteric). Therefore, option A is too general.
    3. Check Position: If you look at a standard periodic table, Beryllium ($Be$) is at the top left, and Aluminum ($Al$) is one row down and one column to the right. This diagonal positioning is the specific reason for their shared chemical behavior.

    Conclusion

    The similarity in properties between Beryllium and Aluminum is a classic example of a diagonal relationship in the periodic table.

    Exam Tip: Remember the mnemonic "L-B-B" for diagonal pairs: Li-Mg, Be-Al, and B-Si. If you see a question about why these specific pairs behave similarly, the answer is almost always "diagonal relationship."

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30. 30.

    A few drops of NaOH solution was added to an unknown salt forming a white precipitate which is insoluble in excess solution. The cation likely present is

    1. A.Zn2+
    2. B.Pb2+
    3. C.Ca2+
    4. D.Al3+

    Show answer

    Answer: C. Ca2+

    AI explanation

    Analysis of the Question

    The question asks us to identify a metal cation based on its reaction with Sodium Hydroxide (NaOH). Specifically, we are looking for a cation that forms a white precipitate that remains insoluble when excess NaOH is added.

    Concept Explanation: Qualitative Analysis of Cations

    In chemistry, we use NaOH to identify metal ions in a solution. When NaOH is added to a solution containing certain metal ions, it forms a metal hydroxide precipitate. The key to this question is the behavior of these precipitates in excess NaOH:

    • Amphoteric Hydroxides: Some metal hydroxides (like those of $Zn^{2+}$, $Pb^{2+}$, and $Al^{3+}$) are amphoteric. This means they can react with both acids and bases. When you add excess NaOH to these, the precipitate dissolves to form a soluble complex (e.g., a zincate or aluminate).
    • Non-amphoteric Hydroxides: Some metal hydroxides (like those of $Ca^{2+}$ and $Mg^{2+}$) are basic and do not react with excess NaOH. Therefore, the white precipitate remains visible even after adding more NaOH.

    Step-by-Step Solution

    1. Evaluate $Zn^{2+}$ (Option A): Adding NaOH to $Zn^{2+}$ forms a white precipitate of $Zn(OH)_2$. This precipitate is amphoteric and dissolves in excess NaOH to form a colorless solution of sodium tetrahydroxozincate(II).
    2. Evaluate $Pb^{2+}$ (Option B): Adding NaOH to $Pb^{2+}$ forms a white precipitate of $Pb(OH)_2$. This is also amphoteric and dissolves in excess NaOH to form a colorless solution of sodium tetrahydroxoplumbate(II).
    3. Evaluate $Ca^{2+}$ (Option C): Adding NaOH to $Ca^{2+}$ forms a white precipitate of $Ca(OH)_2$. Calcium hydroxide is not amphoteric; it does not react with excess NaOH, so the white precipitate remains insoluble.
    4. Evaluate $Al^{3+}$ (Option D): Adding NaOH to $Al^{3+}$ forms a white gelatinous precipitate of $Al(OH)_3$. This is amphoteric and dissolves in excess NaOH to form a colorless solution of sodium tetrahydroxoaluminate(III).

    Conclusion

    Since $Zn^{2+}$, $Pb^{2+}$, and $Al^{3+}$ all form precipitates that dissolve in excess NaOH, only $Ca^{2+}$ fits the description of forming a white precipitate that is insoluble in excess NaOH.

    Exam Tip

    Remember the acronym "ZAP" for cations that form precipitates which dissolve in excess NaOH: Zinc ($Zn^{2+}$), Aluminium ($Al^{3+}$), and Plead ($Pb^{2+}$). If you see these in a question about "excess NaOH," you know they will dissolve!

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31. 31.

    Calculate the quantity of electricity in coulombs required to liberate 10g of copper from a copper compound [Cu=64, F = 96500 C$mol^{-1}$]

    1. A.32395.5
    2. B.30156.3
    3. C.60784.5
    4. D.15196.5

    Show answer

    Answer: B. 30156.3

    AI explanation

    Analysis

    To solve this problem, we need to use Faraday’s Laws of Electrolysis. We are given the mass of the substance to be liberated, its molar mass, and the Faraday constant. We need to find the total charge ($Q$) in Coulombs.

    Concept

    The reaction for the deposition of copper from a copper(II) compound is:

    $Cu^{2+} + 2e^- \rightarrow Cu(s)$

    From this equation, we see that 2 moles of electrons are required to deposit 1 mole of copper.

    • 1 mole of electrons = 1 Faraday ($F$) = 96,500 Coulombs.
    • Therefore, 2 moles of electrons = $2 \times 96,500$ Coulombs.

    Step-by-Step Solution

    Step 1: Determine the number of moles of copper.

    $\text{Moles} = \frac{\text{mass}}{\text{molar mass}} = \frac{10\text{g}}{64\text{g/mol}}$

    $\text{Moles} = 0.15625 \text{ mol}$

    Step 2: Determine the quantity of electricity required. Since 1 mole of Cu requires $2 \times 96,500$ C:

    $\text{Quantity (Q)} = \text{moles} \times \text{valency} \times F$

    $Q = 0.15625 \times 2 \times 96,500$

    $Q = 0.3125 \times 96,500$

    $Q = 30,156.25 \text{ C}$

    Rounding to one decimal place as seen in the options, we get 30,156.3 C.

    Conclusion

    Comparing our result to the provided options, the calculated value matches option B.

    Exam Tip

    Always check the valency of the metal in the compound. If the question had said "Copper(I) chloride," the valency would be 1, and you would not multiply by 2. Since it says "copper compound" without specifying, and copper is typically $Cu^{2+}$ in common electrolysis problems, using a valency of 2 is the standard approach.

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32. 32.

    The process of converting linear alkanes to branched chain and cyclic hydrocarbons by heating in the presence of a catalyst to improve the quality of petrol is referred to as

    1. A.refining
    2. B.cracking
    3. C.reforming
    4. D.blending

    Show answer

    Answer: C. reforming

    AI explanation

    Analysis

    The question asks for the specific industrial process used to convert straight-chain (linear) alkanes into branched-chain or cyclic hydrocarbons. This process is primarily used in the petroleum industry to increase the "octane rating" of petrol (gasoline), making it burn more efficiently in engines.

    Concept Explanation

    To understand this, let's look at the options provided:

    • Refining: This is the broad, general term for the entire process of separating crude oil into various useful products (like petrol, kerosene, and diesel) through fractional distillation.
    • Cracking: This involves breaking down large, heavy hydrocarbon molecules into smaller, more useful ones (like petrol). It is usually done by heat (thermal cracking) or using a catalyst (catalytic cracking).
    • Reforming (Catalytic Reforming): This is a specific chemical process where low-quality, straight-chain alkanes are rearranged into branched-chain alkanes or cyclic hydrocarbons (like benzene). Because branched and cyclic hydrocarbons have higher octane numbers than linear ones, this process significantly improves the quality of petrol.
    • Blending: This is the final stage where different components are mixed together to achieve the desired properties for the final fuel product.

    Step-by-Step Solution

    1. Identify the goal: The goal is to improve the quality of petrol by changing the structure of linear alkanes into branched or cyclic forms.
    2. Evaluate the mechanism: • Cracking breaks chains (making them smaller). • Reforming rearranges the structure (making them more compact/branched/cyclic without necessarily changing the number of carbon atoms significantly).
    3. Match with the definition: The specific industrial term for the rearrangement of hydrocarbon structures to improve fuel quality is Catalytic Reforming.

    Conclusion

    The process described is the definition of reforming.

    Tip: Think of "Reforming" as "re-forming" the molecule into a better shape. If you see "breaking" in a question, think "Cracking." If you see "rearranging" or "improving quality/octane," think "Reforming."

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33. 33.

    If the difference in electronegativity of elements P and Q is 3.0. The bond that will be formed between them is

    1. A.metallic
    2. B.covalent
    3. C.co-ordinate
    4. D.ionic

    Show answer

    Answer: D. ionic

    AI explanation

    1. Analyze the question

    The question asks for the type of chemical bond formed between two elements, P and Q, given that the difference in their electronegativity values is 3.0.

    2. Explain the concept

    Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons. The difference in electronegativity ($\Delta EN$) between two bonded atoms determines the nature of the bond:

    • Non-polar Covalent Bond: $\Delta EN$ is usually between 0 and 0.4. Electrons are shared equally.
    • Polar Covalent Bond: $\Delta EN$ is between 0.5 and 1.7. Electrons are shared unequally.
    • Ionic Bond: $\Delta EN$ is generally greater than 1.7 to 2.0. In this case, the difference is so large that the more electronegative atom completely "steals" the electron from the less electronegative atom, resulting in the formation of ions.

    3. Show the solution

    • Given: Difference in electronegativity ($\Delta EN$) = 3.0.
    • Threshold: In chemistry, a $\Delta EN$ value greater than 1.7 is widely accepted as the threshold for an ionic bond.
    • Reasoning: Since 3.0 is significantly higher than 1.7, the bond between elements P and Q is strongly ionic. The element with the higher electronegativity will pull the bonding electrons completely toward itself, creating a strong electrostatic attraction between the resulting positive and negative ions.

    4. Identify the answer

    Comparing our result to the given options: A. Metallic B. Covalent C. Co-ordinate D. Ionic

    The correct option is D.

    5. Tip

    Memory Trick: Think of the "1.7 Rule." If the difference is less than 1.7, it's Covalent (sharing). If the difference is greater than 1.7, it's Ionic (transferring). Since 3.0 is much larger than 1.7, it is definitely ionic!

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34. 34.

    200 cm3 of a gas at 25ºC exerts a pressure of 700 mmHg. Calculate its pressure if its volume increase 350 cm3 at 75ºC.

    1. A.342.53 mmHg
    2. B.1430.54 mmHg
    3. C.467.11 mmHg
    4. D.400.00 mmHg

    Show answer

    Answer: C. 467.11 mmHg

    AI explanation

    Analysis

    This problem involves the behavior of a fixed mass of gas under changing conditions of pressure, volume, and temperature. To solve this, we use the General Gas Law (also known as the Combined Gas Law).

    Concept

    The Combined Gas Law states that for a fixed amount of gas:

    $\frac{P_1V_1}{T_1} = \frac{P_2V_2}{T_2}$

    Where:

    • $P_1, V_1, T_1$ are the initial pressure, volume, and temperature.
    • $P_2, V_2, T_2$ are the final pressure, volume, and temperature.

    Important Note: In gas law calculations, temperature must always be converted from Celsius (°C) to Kelvin (K) by adding 273.15 (or 273 for JAMB purposes).

    Step-by-Step Solution

    1. Identify the given values:

    • $P_1 = 700 \text{ mmHg}$
    • $V_1 = 200 \text{ cm}^3$
    • $T_1 = 25^\circ\text{C} = 25 + 273 = 298 \text{ K}$
    • $V_2 = 350 \text{ cm}^3$
    • $T_2 = 75^\circ\text{C} = 75 + 273 = 348 \text{ K}$
    • $P_2 = ?$

    2. Rearrange the formula to solve for $P_2$:

    $P_2 = \frac{P_1 \times V_1 \times T_2}{V_2 \times T_1}$

    3. Substitute the values into the equation:

    $P_2 = \frac{700 \times 200 \times 348}{350 \times 298}$

    4. Perform the calculation:

    • Numerator: $700 \times 200 \times 348 = 48,720,000$
    • Denominator: $350 \times 298 = 104,300$
    • $P_2 = \frac{48,720,000}{104,300} \approx 467.114 \text{ mmHg}$

    Rounding to two decimal places, we get 467.11 mmHg.

    Conclusion

    Comparing our result with the given options, the correct value is 467.11 mmHg.

    Exam Tip

    Always remember to convert your temperature to Kelvin! A common mistake students make in JAMB is using the temperature in Celsius directly, which will lead to an incorrect answer. Also, check your units—since the pressure is requested in mmHg and the initial pressure is in mmHg, no unit conversion is needed for pressure.

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35. 35.

    A silicon -containing ore has 92% 28Si, 5% 29Si and 3% 30Si. Calculate the relative atomic mass of the silicon.

    1. A.14.00
    2. B.29.00
    3. C.28.11
    4. D.28.00

    Show answer

    Answer: C. 28.11

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36. 36.

    The basicity of CH3COOH is

    1. A.4
    2. B.1
    3. C.2
    4. D.3

    Show answer

    Answer: B. 1

    AI explanation

    Analysis

    The question asks for the basicity of ethanoic acid ($CH_3COOH$). In chemistry, the basicity of an acid refers to the number of replaceable hydrogen ions ($H^+$) that one molecule of the acid can release in an aqueous solution.

    Concept Explanation

    • Basicity of an acid: This is determined by the number of ionizable hydrogen atoms present in the carboxyl group ($-COOH$) of an organic acid.
    • Structure of Ethanoic Acid ($CH_3COOH$): Although the formula contains four hydrogen atoms, only the hydrogen atom attached to the oxygen in the carboxyl group ($-COOH$) is acidic. The three hydrogen atoms attached to the carbon atom ($CH_3-$) are covalently bonded and do not dissociate in water.
    • Dissociation: When ethanoic acid dissolves in water, it ionizes as follows: $$CH_3COOH_{(aq)} \rightleftharpoons CH_3COO^-_{(aq)} + H^+_{(aq)}$$Since only one$H^+$ ion is produced per molecule, the acid is monobasic.

    Step-by-Step Solution

    1. Identify the functional group: Ethanoic acid belongs to the carboxylic acid family, characterized by the $-COOH$ group.
    2. Determine ionizable hydrogens: In carboxylic acids, only the hydrogen in the $-COOH$ group is replaceable by a metal or a base.
    3. Count the replaceable hydrogen: There is only one such hydrogen atom in $CH_3COOH$.
    4. Conclusion: Since it releases only one $H^+$ ion, its basicity is 1.

    Identifying the Answer

    Comparing our result to the given options: A. 4 B. 1 C. 2 D. 3

    The correct option is B.

    Exam Tip

    Always remember: Basicity is for acids (number of $H^+$), and Acidity is for bases (number of $OH^-$). For organic acids like $CH_3COOH$, $HCOOH$, or $C_2H_5COOH$, the basicity is almost always 1 because they only contain one $-COOH$ group. Don't be tricked by the total number of hydrogen atoms in the formula!

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37. 37.

    The radio active radiation used in studying the arrangement of particles in giant organic molecules is

    1. A.$\gamma$- rays
    2. B.$\alpha$- particles
    3. C.X-rays
    4. D.$\beta$ - particles

    Show answer

    Answer: C. X-rays

    AI explanation

    Analysis

    The question asks for the specific type of radiation used to determine the structural arrangement of atoms within complex (giant) organic molecules, such as proteins or polymers. This process is known as X-ray crystallography (or X-ray diffraction).

    Concept Explanation

    To study the arrangement of particles (atoms) in a molecule, the wavelength of the radiation used must be comparable to the distance between the atoms in the molecule (which is typically in the range of $10^{-10}$ meters or 1 Angstrom).

    • X-rays have wavelengths in the range of $0.01$ to $10$ nanometers, which perfectly matches the inter-atomic spacing in crystals. When X-rays strike a crystal, they are diffracted by the atoms, creating a pattern that scientists can analyze to map out the exact positions of atoms in a giant molecule.
    • $\alpha$-particles are heavy, positively charged helium nuclei that do not penetrate matter well enough for structural analysis.
    • $\beta$-particles are high-energy electrons that are typically used for medical imaging or dating, but they are not suitable for diffraction studies of molecular structures.
    • $\gamma$-rays have extremely short wavelengths and high energy; they are generally too penetrating and difficult to focus for the precise structural determination required for organic molecules.

    Step-by-Step Solution

    1. Identify the objective: We need a radiation type that can diffract off atoms to reveal their spatial arrangement.
    2. Evaluate the options: • $\alpha$ and $\beta$ particles are matter particles, not electromagnetic waves, and are unsuitable for diffraction patterns of molecular structures. • $\gamma$-rays have wavelengths that are too short and energy levels that are too high, often causing damage to the sample rather than providing a clear diffraction pattern. • X-rays have the ideal wavelength to interact with the electron clouds of atoms in a crystal lattice.
    3. Conclusion: X-ray diffraction is the standard scientific method for determining the 3D structure of giant organic molecules (like the famous discovery of the DNA double helix structure).

    Correct Answer

    The correct option is C.

    Exam Tip

    Whenever you see a question about "determining the structure of molecules," "crystal lattice," or "atomic arrangement," always look for X-rays or X-ray diffraction. It is a classic JAMB Chemistry topic!

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38. 38.

    In a chemical reaction, the change in concentration of a reactant with time is

    1. A.entropy of reaction
    2. B.enthalpy of reaction
    3. C.rate of reaction
    4. D.order of reaction

    Show answer

    Answer: C. rate of reaction

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39. 39.

    16.55g of lead (ll) trioxonitrate (V) was dissolved in 100g of distilled water at 20oC, calculate the solubility of the solute in mol$dm^{-3}$ [Pb = 207, N = 14, O = 16]

    1. A.0.05 g
    2. B.2.00 g
    3. C.1.00 g
    4. D.0.50g

    Show answer

    Answer: D. 0.50g

    AI explanation

    To solve this problem, we need to determine the concentration of the solution in moles per cubic decimeter ($mol/dm^3$).

    1. Analyze the Question

    • Mass of solute ($m$): 16.55 g
    • Mass of solvent (water): 100 g
    • Molar Mass of $Pb(NO_3)_2$: We need to calculate this using the given atomic masses ($Pb=207, N=14, O=16$).
    • Goal: Calculate solubility in $mol/dm^3$.

    2. Explain the Concept

    Solubility in $mol/dm^3$ is calculated using the formula:

    $\text{Concentration} = \frac{\text{Number of moles}}{\text{Volume of solution in } dm^3}$

    Since the mass of the solute is small compared to the water, we assume the volume of the solution is approximately equal to the volume of the water. Given that the density of water is $1 g/cm^3$, $100 g$ of water is equal to $100 cm^3$ (or $0.1 dm^3$).

    3. Show the Solution

    Step 1: Calculate the Molar Mass of $Pb(NO_3)_2$

    • $Pb = 207$
    • $N = 14 \times 2 = 28$
    • $O = 16 \times 6 = 96$
    • Total Molar Mass = $207 + 28 + 96 = 331 g/mol$

    Step 2: Calculate the number of moles ($n$)

    $n = \frac{\text{mass}}{\text{molar mass}}$

    $n = \frac{16.55}{331} = 0.05 \text{ moles}$

    Step 3: Convert volume to $dm^3$ Volume = $100 cm^3 = \frac{100}{1000} dm^3 = 0.1 dm^3$

    Step 4: Calculate the concentration

    $\text{Concentration} = \frac{0.05 \text{ mol}}{0.1 dm^3} = 0.5 \text{ mol/dm}^3$

    4. Identify the Answer

    Comparing our result ($0.5$) to the options provided, the correct value is $0.50$. Note that while the unit in the question asks for $mol/dm^3$, the options are labeled with 'g'. Based on the calculation, the numerical value is 0.50.

    5. Exam Tip

    When dealing with solubility questions in JAMB, always remember the conversion factor: $1000 cm^3 = 1 dm^3$. If you are given the mass of water in grams, it is almost always safe to treat it as the volume in $cm^3$ for these calculations unless the density of the solution is provided.

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40. 40.

    $H_2O_{(g)} + C_{(s)} → H_{2(g)} + CO_{(g)}$ The oxidizing agent in the reaction above is

    1. A.CO(g)
    2. B.C(s)
    3. C.H2O(g)
    4. D.H(2)(g)

    Show answer

    Answer: C. H2O(g)

    AI explanation

    Analysis of the Question

    The question asks us to identify the oxidizing agent in the chemical reaction: $H_2O_{(g)} + C_{(s)} \rightarrow H_{2(g)} + CO_{(g)}$

    Explaining the Concept

    To identify the oxidizing agent, we must track the changes in the oxidation states of the elements involved:

    1. Oxidation: This is the gain of oxygen, loss of hydrogen, or an increase in oxidation number. The substance that undergoes oxidation is called the reducing agent.
    2. Reduction: This is the loss of oxygen, gain of hydrogen, or a decrease in oxidation number. The substance that undergoes reduction is called the oxidizing agent.

    Assigning Oxidation Numbers:

    • In $H_2O$: Hydrogen is $+1$, Oxygen is $-2$.
    • In $C$ (elemental state): Oxidation number is $0$.
    • In $H_2$ (elemental state): Oxidation number is $0$.
    • In $CO$: Carbon is $+2$, Oxygen is $-2$.

    Step-by-Step Solution

    1. Track Carbon ($C$): Carbon goes from $0$ (in $C_{(s)}$) to $+2$ (in $CO_{(g)}$). Since its oxidation number increased, Carbon is oxidized. Therefore, Carbon acts as the reducing agent.
    2. Track Hydrogen ($H$): Hydrogen goes from $+1$ (in $H_2O$) to $0$ (in $H_2$). Since its oxidation number decreased, Hydrogen is reduced.
    3. Identify the Oxidizing Agent: Because $H_2O$ provides the oxygen that oxidizes the carbon and contains the hydrogen that gets reduced, $H_2O$ is the substance that causes oxidation. Therefore, $H_2O$ is the oxidizing agent.

    Conclusion

    The substance that is reduced is the oxidizing agent. Since $H_2O$ is reduced to $H_2$, it is the oxidizing agent.

    Exam Tip

    A simple way to remember this is the acronym OIL RIG:

    • Oxidation Is Loss (of electrons/increase in oxidation state).
    • Reduction Is Gain (of electrons/decrease in oxidation state). The substance that gets reduced is the oxidizing agent, and the substance that gets oxidized is the reducing agent.

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41. 41.

    What is the percentage of sulphur in sulphur (IV) oxide?

    1. A.66%
    2. B.25%
    3. C.40%
    4. D.50%

    Show answer

    Answer: D. 50%

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42. 42.

    The mathematical expression of PH is

    1. A.log 10[OH-]
    2. B.log 101/[H 3 O+]
    3. C.log 10[H 3 O+]
    4. D.log 101/[OH -]

    Show answer

    Answer: B. log 101/[H 3 O+]

    AI explanation

    Analysis

    The question asks for the correct mathematical definition of pH. In chemistry, pH is a measure of the acidity or basicity of an aqueous solution, specifically representing the concentration of hydrogen ions (or hydronium ions, $H_3O^+$) in that solution.

    Concept Explanation

    The pH scale is defined as the negative logarithm (base 10) of the hydrogen ion concentration. Mathematically, this is expressed as:

    $pH = -\log_{10}[H^+]$

    or, since $H^+$ ions exist in water as hydronium ions ($H_3O^+$):

    $pH = -\log_{10}[H_3O^+]$

    Using the laws of logarithms, specifically the rule that $-\log(x) = \log(\frac{1}{x})$, we can rewrite the expression:

    $pH = \log_{10}\left(\frac{1}{[H_3O^+]}\right)$

    Step-by-Step Solution

    1. Identify the standard definition: $pH = -\log_{10}[H_3O^+]$.
    2. Apply logarithm rules: The negative sign in front of the log allows us to take the reciprocal of the value inside the bracket.
    3. Transform the expression: $-\log_{10}[H_3O^+]$ becomes $\log_{10}\left(\frac{1}{[H_3O^+]}\right)$.
    4. Compare with options: • Option A: $\log_{10}[OH^-]$ (This relates to pOH, not pH). • Option B: $\log_{10}\frac{1}{[H_3O^+]}$ (This matches our derived expression). • Option C: $\log_{10}[H_3O^+]$ (This is missing the negative sign or the reciprocal). • Option D: $\log_{10}\frac{1}{[OH^-]}$ (This relates to pOH).

    Exam Tip

    Always remember that "p" in pH stands for "power" or "potential," which mathematically translates to the negative log ($-\log$). If you see a "p" in front of a concentration (like pOH or pKa), it always means $-\log$ of that concentration. If you prefer to write it without the negative sign, you must use the reciprocal ($1/concentration$).

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43. 43.This question needs a diagram, table or passage that we don't have yet, so it isn't shown.

44. 44.

    On exposure to the atmosphere, a hydrated salt loses its water of crystallization to become anhydrous. This phenomenon is referred to as

    1. A.efflorescence
    2. B.deliquescence
    3. C.hygroscopy
    4. D.hydrolysis

    Show answer

    Answer: A. efflorescence

    AI explanation

    Analysis

    The question asks for the specific term used to describe the process where a hydrated salt loses its water of crystallization when exposed to the atmosphere, resulting in the salt becoming anhydrous (or forming a lower hydrate).

    Concept Explanation

    In chemistry, the interaction between salts and atmospheric water vapor (or lack thereof) is categorized into three main phenomena:

    1. Efflorescence: This occurs when a hydrated salt has a higher water vapor pressure than the surrounding atmosphere. Consequently, the salt loses its water of crystallization to the air and becomes a powder or anhydrous.
    2. Deliquescence: This is the opposite of efflorescence. It occurs when a substance absorbs so much moisture from the atmosphere that it eventually dissolves in the absorbed water to form a solution.
    3. Hygroscopy: This refers to substances that absorb moisture from the atmosphere without necessarily dissolving in it. They are often used as drying agents (desiccants).
    4. Hydrolysis: This is a chemical reaction where water is used to break down the bonds of a particular substance. It is not related to the physical loss of water of crystallization.

    Step-by-Step Solution

    • Step 1: Identify the key action in the question: "loses its water of crystallization."
    • Step 2: Evaluate the options based on the definitions above.
    • Step 3: Since the salt is losing water to the atmosphere, it matches the definition of efflorescence.

    Exam Tip

    To remember the difference, think of "E" for Efflorescence = Exiting (water is exiting the salt). Think of "D" for Deliquescence = Dissolving (the salt is dissolving into a liquid).

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45. 45.

    How many faraday of electricity is required to produce 0.25 mole of copper?

    1. A.1.00F
    2. B.0.01F
    3. C.0.05F
    4. D.0.50F

    Show answer

    Answer: D. 0.50F

    AI explanation

    Analysis

    To solve this problem, we need to understand the relationship between the amount of electricity (in Faradays) and the number of moles of metal deposited during electrolysis. This is based on Faraday's First Law of Electrolysis.

    Concept

    The reduction of copper ions ($Cu^{2+}$) to copper metal ($Cu$) occurs according to the following half-equation:

    $Cu^{2+}_{(aq)} + 2e^- \rightarrow Cu_{(s)}$

    From this equation, we can see that:

    • 1 mole of copper requires 2 moles of electrons to be deposited.
    • Since 1 mole of electrons carries a charge of 1 Faraday (F), it follows that 1 mole of copper requires 2 Faradays of electricity.

    Solution

    Step 1: Identify the stoichiometry. As shown in the equation above, 1 mole of $Cu$ requires 2 Faradays of electricity.

    Step 2: Set up the calculation. We are asked to find the electricity required for 0.25 mole of copper. We use the ratio:

    $\text{Electricity} = \text{Moles of Cu} \times \text{Faradays per mole}$

    $\text{Electricity} = 0.25 \text{ mol} \times 2 \text{ F/mol}$

    Step 3: Calculate the result.

    $\text{Electricity} = 0.50 \text{ F}$

    Conclusion

    The amount of electricity required to produce 0.25 mole of copper is 0.50 Faraday. This matches option D.

    Exam Tip

    Always write out the half-equation for the metal being deposited. The coefficient of the electrons ($e^-$) tells you exactly how many Faradays are needed to produce 1 mole of that metal. For monovalent ions (like $Ag^+$), it's 1F; for divalent ions (like $Cu^{2+}$ or $Zn^{2+}$), it's 2F; and for trivalent ions (like $Al^{3+}$), it's 3F.

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